In recent years, increasingly higher needs exist for human harmonized, coexistent robots and information equipment which can be utilized in life support. It is necessary to have a coexistent robot recognize the environment and human actions, and human's visual system must be systematically implemented for tracking a moving object with eyes. Also, with an increase in the crime rate, demands have been increased for systems which are capable of accurately and rapidly acquiring information on a moving person, such as a monitoring camera and a video surveillance for examining recorded video images.
A number of studies have been already made on technologies for automatically tracking a moving object, which is required in applications as described above. There are a method of extracting and tracking an area of a moving object which is a target by extracting edge portions of the moving object from inter-frame differential images, a method of selecting an area of a moving object comprised of pixels which present a large flow, using an optical flow which is a velocity vector indicating how far and in which direction a point or a figure in an image will move at a next instance, and the like.
For example, the following Patent Document 1 discloses an object tracking method which uses both of an optical flow and motion information based on a correlation (matching) with a template image.    Patent Document 1: JP2004-240762A